British Columbia
HOW DRAWING REVISIONS WORK ACROSS A FAMILY OF PARTS
A drawing revision records a change, and a new part number marks a version that no longer swaps in for the old one.
Drawing revision control keeps every version of a bracket, guard, or panel you reorder apart, so the right one gets made, shelved, and fitted. A change gets the next revision letter as long as the new version still swaps in for the old one. If it no longer does, it needs a new part number. "Swaps in" means the new version fits and works anywhere the old one did, without filing, drilling, or changing the parts around it. This guide covers that choice, the drawing's revision block, related sizes and assemblies, old stock, and what to write on the order.
The test is whether the new version can replace the old one in every machine that uses it. Large manufacturers write this rule into their drawing standards, and it works the same for a short run of brackets.
| The change | Does the new version still swap in? | What it gets |
|---|---|---|
| The drawing is redrawn or tidied, and nothing about the part itself changes | Yes, nothing changed | No new letter, because every part made from it is identical |
| A tolerance is tightened, and the old stock already meets it | Yes | The next revision letter, with that dimension checked on the first part |
| A slot is lengthened, and it still bolts to every machine | Yes | The next revision letter, with the slot checked on the first part |
| Galvanized becomes stainless, with the same size and holes | Only if galvanized still does the job in every machine | The next letter if it does, and a new part number if it doesn't |
| A new bolt pattern means older machines can't take it | No | A new part number |
| A new design fits only the new model, and the old version fits only older ones | No | A new part number, with the old one kept for spares |
If you're not sure whether a change still swaps in, treat it as a new part number. A new number costs nothing, and a guard that doesn't fit can stop a machine.
Four terms carry drawing revision control. Each one answers a different question.
It names the item and stays the same while each new version still swaps in. Keep the revision letter out of it, because "GD-410C" reads as a different item in stock.
It moves up each time the drawing changes what gets made. Order by part number and letter together, and the shop knows exactly which version to make.
The document that records a change, called a change order or change notice. Send one with every changed drawing, saying what changed, why, and what happens to old stock.
The order, lot, serial number, or date from which the new version is used. Without it, nobody knows which machines get the old version and which get the new one.
First Article Inspection for Sheet Metal Parts explains how to check the first part after a change, and when to sign a new sample.
The revision block is the small table, usually in a top corner of the drawing, that lists every change since the drawing was first released. A reader should be able to tell from it what changed between any two versions.
| Column | What goes in it | Why it matters |
|---|---|---|
| Revision letter | The letter this change created | It matches the letter in the title block, the box with the part number, and on the order |
| Description | What changed, in a few words, or the number of the change notice | The shop can see what's different without comparing two drawings line by line |
| Zone | The grid square on the drawing where the change sits | The changed feature is found in seconds on a busy sheet |
| Date | When the change was approved | Anyone holding an old print can tell how current it is |
| Approved by | The person who signed off the change | Anyone with a question knows who to ask |
The first release is often marked with a dash or the letter A, and some companies use numbers. Drawings made to the American standard, ASME Y14.35, skip the letters I, O, Q, S, X, and Z. ISO drawings skip only I and O. Once the single letters run out, the next revision is AA.
The revision block lists every change, and the title block shows the current letter
Illustration of guard GD-410, from first release through two changes. The part number stays because each version still swaps in.
| Rev | Description | Zone | Date | Approved |
|---|---|---|---|---|
| A | First release | date | initials | |
| B | Mounting slots lengthened | C3 | date | initials |
| C | Corners rounded for safer handling | date | initials |
A new bolt pattern that older machines can't take would not become revision D. It gets a new part number, GD-411, with its own revision A.
Illustration, not a real part.
A repeat bracket rarely lives on its own, because it may come in four sizes, sit inside an assembly, and fit three models. That means one change to it can reach well beyond the bracket itself.
A tabulated drawing covers a family of sizes, each with a dash number such as -1, -2, and -3. If you add a size, give it a new dash number and never reuse an old one, so past orders still point to the right size.
If a bracket gets a new part number, the assembly it goes into gets one too. Renumber each level above it, up to the first one that still swaps in.
Before you change anything, list every assembly and machine model that uses it. If one of them can't take the new version, that's a new part number.
Knowing which version of each part sits in which machine is called configuration management, and ISO 10007 sets out how to do it.
A drawing change rarely lands on an empty shelf. Decide what happens to the old stock when you approve the change, and put it on the order.
| What to do with old parts | When to choose it | What to write on the order |
|---|---|---|
| Use them up first | The old version still swaps in and works, and the change is an improvement | "PN-330, revision D from this order on. We'll fit our revision C stock first" |
| Have them reworked | The old stock can be changed to match the new drawing, such as a hole added | "Rework 40 PN-330 revision C panels to revision D, quote separately" |
| Scrap them | The old version is unsafe or won't work in any machine you still support | "PN-330 revision C is withdrawn. Scrap remaining stock" |
| Keep them as spares | The old version fits older machines the new one can't | "Old part keeps GD-410. New part is GD-411" |
The "from this order on" in the first row is the effectivity. Name it every time, so the fabricator and your stockroom know where the old version stops.
Machines in the field outlive their drawings. A fleet or equipment maker still needs the right spare for a unit built five revisions ago.
When a new part number replaces an old one, mark the old drawing as replaced and keep it. Spares for older machines are then made from it.
If the new version can't fit older machines, it gets a new part number. The old number stays with the old design, and spares orders stay clear.
Note it on each machine's build record. When a part wears out, order the current letter of that number, since every letter of it swaps in.
Order a spare from the drawing on file, not from the worn part's sizes. A worn edge shows where it failed, not the size it started at.
When a worn part should be repaired and when it should be made new is covered in Repair or Remake a Worn Fabricated Part.
A drawing tells you which version is current. A mark on the metal tells you which version is in your hand.
If loose stock could get mixed on a shelf, ask for the part number and letter on each one or its bag. Say on the drawing how and where it's marked.
Put the mark where the finish won't cover it, or add it after coating. A mark under the coat helps nobody on the shop floor.
This example follows one guard from its first release to a new part number. The guard and the order numbers are an illustration, not a customer's order.
| Change | Swaps in? | Result | What the order said |
|---|---|---|---|
| First release of guard GD-410 | Not applicable | Revision A | "GD-410, revision A, 60 pieces" |
| Mounting slots lengthened for easier fitting | Yes | Revision B, slots checked on the first part | "GD-410, revision B from this order on. We'll fit our revision A stock first" |
| Corners rounded so fitters don't cut their hands | Yes | Revision C | "GD-410, revision C from this order on. Revision B stock is still fine to fit" |
| A new machine model needs a different bolt pattern | No | New part GD-411, revision A | "GD-411, revision A, 30 pieces. GD-410 stays in production for older machines" |
The last row is the one that goes wrong most often. Calling the new guard "GD-410, revision D" would let it land on an older machine it can't fit.
Most mix-ups trace back to a missing letter, a reused part number, or an old drawing still in use. Each row below shows one.
| Mistake | What happens | Do this instead |
|---|---|---|
| Ordering by part number alone | The shop may make the version it last made, not the current one | Put the part number and revision letter on every order |
| Building the letter into the part number | "GD-410C" reads as a different item in stock and on orders | Keep them apart, as "GD-410, revision C" |
| Keeping the part number on a part that no longer swaps in | The new version gets fitted to a machine it can't serve | Give it a new part number |
| Sending a new drawing with no word on old stock | Old and new versions sit in the same bin | Say on the order what happens to the old parts |
| An old drawing still saved in an email thread | Someone quotes or orders from the wrong version | Send the current drawing with each order, and mark old copies as replaced |
| A new letter with a blank description | Nobody can tell what changed without comparing two drawings | Write what changed in the revision block every time |
Repeat orders are made on our floor in Pitt Meadows, and every order is tied to one drawing and one revision letter. These steps keep it that way from the first quote to the latest reorder.
We check the revision letter before quoting. If your order's letter doesn't match our drawing, we ask before pricing anything.
Changes after approval come in writing. After you approve the drawings, changes to metal, sizes, bends, hardware, or finish get a written revision first.
A change to fit gets a new first part. If we've agreed you'll sign a sample, it comes to you before the run.
We check the letter before parts leave. Each part is checked against the drawing, including its revision letter, before release.
We keep the drawing on file. The approved drawing and its letter stay with us, so the next order starts from the right version.
If a batch is made to the wrong letter and the mistake was ours, we fix or remake it at no charge. What Happens After Shop Drawing Approval explains why a late change costs more.
A fabricator can make every version you approve and keep them apart. The engineering call on whether a change is safe stays with whoever owns the design.
If an order's letter and a drawing disagree, we'll stop and ask rather than guess. A short phone call beats a batch made for last year's machine.
Our custom metal supports and enclosures page covers brackets, guards, and stands for equipment. The bending behind them is shown on sheet metal cutting and bending.
A changed design needs a little more on the order than a plain reorder. Each item below saves a phone call later.
For a reorder with no change, Sheet Metal Prototype to Production has the short version. More guides for repeat parts are in OEM, Prototype and Repeat Production.
A drawing with a full revision block and a marked-up print with a note in the margin are both a fine place to start. We'll tell you what's unclear before the first part of the new version is cut.
Standard ductwork and fittings price instantly on WebDuct, the online pricing and ordering portal, with a company account. Prototypes, production parts, stainless, and other custom work start with a request or a call.
At Duct Duct Goose, we specialize in sheet metal fabrication and stainless steel services for commercial and industrial applications, including HVAC systems, ducts, and custom metalwork. Please note that we do not offer services for automotive-related projects, such as vehicle parts, repairs, or modifications.
